Hi Schabelf, is this a correct description of the problem:

• Using "Open" in the download dialog => error
• Using "Save" in the download dialog, then (outside of Firefox) open from the downloads folder => okay
• Using "Save" in the download dialog, then open from the downloads arrow toolbar button => error?

Firefox 68 has a new startup process where instead of running with administrative privileges -- for users with admin privileges -- it runs with standard user privileges. This helps protect against unwanted system changes. However, when you launch a helper program from inside Firefox that program may inherit the lower privileges of Firefox (standard instead of admin). Not all programs can deal with that.

Workaround?

If that theory is correct, there is a workaround to force Firefox to run with your full user privileges. Whether you decide to do this depends on how much of an inconvenience this is for you versus the security benefits of the browser being able to do less damage to the system if it becomes compromised.

You could test it to see whether my theory is the explanation. If not, it must be something else.

Here's how:

The simplest method would be to modify your Firefox program shortcut (assuming you start Firefox from the program shortcut, and not from a link). Either:

• Right-click a Firefox desktop shortcut, then click Properties
• Right-click a Firefox icon pinned to the Taskbar then right-click Mozilla Firefox, then click Properties

Windows should show the Shortcut tab and select the Target field. The Target usually is along the following lines:

• "C:\Program Files\Mozilla Firefox\firefox.exe"
• "C:\Program Files (x86)\Mozilla Firefox\firefox.exe"

You would add a space and then the new switch, either:

• "C:\Program Files\Mozilla Firefox\firefox.exe" -no-deelevate
• "C:\Program Files (x86)\Mozilla Firefox\firefox.exe" -no-deelevate

This will take effect the next time you exit out of Firefox and start it up again using the shortcut. Any difference?

Your description of the problem is correct. I tried your solution and it did not fix the problem. Mrs Pam Ericson, the tech support person who has been helping me at Mastercook support, tried downloading and opening MC recipe files on her computer using same version of Firefox and could not duplicate the problem. Very strange. No changes to my computer recently except routine updates to Windows 10, Firefox etc. I love computers but I am old and was not raised with them so don’t know much about dll files like the one giving this error or programming. All I know is that these recipe files are .mz2 files which are set in my computer to open with Mastercook which they do outside of Firefox.